In electronic products such as automobiles, meters and watches, a precise and micro-stepping motor is necessary. FIG. 1 illustrates a structural scheme of a stepping motor 100 as published in U.S. Pat. No. 4,371,821. The stator 101 of this stepping motor 100 is a stator blade made of soft magnetic materials and has the profile of an isosceles trapezoid, whose center position is a rotor hole accommodating the rotor. The center position of the bottom edge of stator 100 has a gap 102a. In addition there are two gaps 102b and 102c surrounding the rotor hole, such that the gaps 102a, 102b and 102c are separated from each other by an angle of 120°, thus forming three magnetic-pole end surfaces 101a, 101b and 101c surrounding the rotor hole. Coils 105 and 106 are equipped on both sides of the stator blade 101.
The rotor of stepping motor 100 is composed of the permanent-magnet rotor 104 and rotor axis 103. Both ends of the rotor axis 103 have gears (not shown) to transfer revolving motion of the rotor.
When a current is applied to coils 105 and 106 in a certain direction (i.e., so as to create magnetic fields in directions 111 and 112, respectively), a magnetic field will be formed between the magnetic-pole end surfaces of the stator blade 101. This magnetic field will be saturated at the gaps 102a, 102b and 102c. As a result, a magnetic field moment will be produced to push the rotor 104 to revolve about axis 103.
The directions of the current in the two coils 105 and 106 can be changed under control of the control circuit (not shown), which can make the motor revolve in steps in single direction. The distances from the three magnetic-pole end surfaces 101a, 101b and 101c to the rotor 104 are variable, and therefore the shape thereof makes the rotor 104 reach a balancing status on the centrosymmetric axis on the bottom side of the isosceles trapezoid. Thus the stepping motor 100 can realize 180° stepped rotation.
This stepping motor 100 has advantages such as stable rotation and high precision. But because its stator blade 101 is very thin, the gaps 102a, 102b and 102c make the stator blade very weak and easy to twist, resulting in increasing difficulties of machining and assembling.